The present invention relates to an arciform photosensor assembly for use in an optical apparatus for measuring the intensity distribution of light scattered forward by particles suspended in a fluid medium.
For instance, among various means for detecting the size distribution of particles, there is known a method based on a theory about the small-angle light scattering by particles suspended in a fluid medium. Conformably to the method an optical system as shown schematically in FIG. 4 is employed in combination with a photosensor assembly as shown in FIG. 5. According to FIG. 4, the optical system consists baiscally of a light source 1 such as a laser, a lens assembly 2 for providing a light beam F having a desired thickness, a transparent flow cell 3 in which a suspension suspending sample particles is made to flow, a Fourier-transform lens 4 and a photodetector 5a made up of an assembly of concentric semicircular photosensors S.sub.i (i=1, 2, . . . , N) as shown in FIG. 5. In the optical system of FIG. 4, the light beam F incident into the flow cell 3 is scattered or diffracted by the sample particles, and then focused circularly on the detector 5 by the Fourier-transform lens 4, thus forming a circular image whose intensity varies in the radial direction. The radial-directional intensity distribution is detected by the above N concentric semicircular photosensors S.sub.i, and then mathematically analized by a mirocomputer (not shown) in accordance with the Mie scattering theory and/or the Fraunhoher diffraction theory to finally give the size distribution of the sample particles.
In such an optical system, that substantially constitutes an apparatus for detecting the intensity distribution of light scattered forward by particles suspended in a fluid medium, it is essentially important to adjust the direction of the light beam B so as to be directed precisely to the common center of the concentric semicircular photosensors S.sub.i. It also is important to adjust the light beam B so as to have a desired thickness. The direction and thickness of the beam B have conventionally been adjusted through directly watching the beam with the eye or by using a special jig. However, the visual method of adjustment is harmful to the eye, while the use of a jig is often troublesome and inconvenient.